Okay, so you're period is late/never came/is on and off like a tap and you're srsly freakin' out.
Don't stress. There are SO many reasons (yes, besides being ~pregnant~) why this could be happening and we're going to give you the low-down.
Stress can cause many unpleasant things, like headaches, weight gain and acne ~but~ it can also effect your monthly flow. When you're under physical or emotional stress, your body produces the stress hormones adrenaline and cortisol.
Elevated levels then force the brain to decide which bodily functions are essential and which are nonessential.
SO, you're body chooses things like, uh, I dunno, sending blood flow to the muscles and oxygen to the lungs over your reproductive cycle.
Whether it be a simple cold or something more serious, again your body switches to "which function do I need most?" mode. So, usually ovulation is delayed, late or nonexistent.
If you feel sick on/around the time of your period, it's most likely that 'Shark Week' will return once things are back to normal.
Your hypothalamus, the gland in your brain responsible for regulating various bodily functions - including your menstrual cycle, is affected by your weight. Extreme weight loss, a low caloric intake or being underweight can all cause your hypothalamus stress, meaning your body won't release the estrogen needed to build the lining in your uterus.
SO, keeping a steady and healthy weight will result in a consistent crimson river.
4. Excessive exercise
Obvi working out is good for you ~but~ when you overdo it your body doesn't have time to produce enough oestrogen.
Side Note: I know what you're thinking - this is not an excuse to not do ANY exercise at all.
5. Change in your routine
Switching things up and getting out of your regular routine can throw your body off balance. Travelling/staying up late/eating irregularly can cause your period to become delayed. Once your body registers the change or your schedule goes back to normal the lady in red should slowly make her way back.
The most common medication to cause menstrual changes is contraception. Hormonal contraceptives such as the pill work by stopping the body from ovulating — and no ovulation means no period.
So next time your late or miss a period make sure you don't ~jump~ to conclusions and remember these!